Experience with a Slow Control system based on industrial process control hardware and software for the XENON1T dark matter search

XENON1T is a next generation Dark Matter search experiment using 3.5 tons of liquid xenon for direct detection of Dark Matter. A dual-phase liquid xenon Time Projection Chamber (TPC) shielded below 1400 m of rock at the Gran Sasso underground laboratory in Italy serves as both target and detector. The TPC is inside a 10 m high by 9.5 m diameter water Cherenkov detector serving as an active muon veto. The Slow Control system is based on industrial process control hardware and software. It is now being used to commission the detector. The system provides secure monitoring and control by collaborators, shifters and experts at both local and remote locations. 3.5 tons of liquid xenon requires extreme care to guard the safety of the instrumentation and to prevent the loss of any of the high value xenon. The system consists of a distributed architecture of networked local control units with touch panels for local control. Critical operations can be guarded by requiring specific conditions to be satisfied before they are allowed to be executed. Two Supervisory Control And Data Acquisition (SCADA) computers provide active-passive redundancy. All operating parameters and their history are stored and can be displayed. Alarm messages are sent by email, cellular network and by pre-recorded voice over land telephone lines. Experience with both the benefits and the disadvantages of using industrial process control hardware and software are presented.